Process of producing a supported platinum metal catalyst



atented July 5, 1949 PROCESS OF PRODUCING A SUPPORTED PLATINUIW METALCATALYST Edgar F. Rcsenblatt, East Orange, N. J., assignor to Baker &Company, Inc., Newark, N. J a corporation of New Jersey No Drawing.Application December 27, 1945, Serial No. 637,483

8 Claims. (Cl. 252-460) This invention relates generally to catalystsand is concerned in particular with the production of supportedcatalysts.

The employment of supported catalysts, comprising a catalyst metal suchas platinum deposited on a carrier, is well known in various catalyticprocesses such, for example, as hydrogenation processes. The activityand performance of such supported catalysts depend on a number offactors, for instance the nature of the catalyst metal and its inherentcatalytic properties, the type of support employed, the method by whichthe catalyst metal is deposited upon the support, etc., and otherfactors, many of which are not clearly understood in their import or thereasons therefor.

Supported platinum metal catalysts are usually produced by providing asolution containing a compound of the platinum metal, bringing thesolution in contact with the support, e. g. by soaking, and reducing theplatinum metal compound by the employment of reducing agents or heat,whereupon the platinum metal is deposited, usually in metallic form,upon the support during the reduction of the compound.

Such methods of producing supported platinum metal catalysts asheretofore practiced are, however, in many cases deficient in that theresultant catalyst does not have maximum catalytic efflciency which inthe production of supported catalysts is the prime object. Also suchmethods are frequently cumbersome and diflicult to practice.

It is therefore one object of this invention to provide a method ofproducing supported platinum metal catalysts which shall be simple andeffective. It is another object of this invention to provide by means ofsuch method a supported platinum metal catalyst which shall have a highcatalytic efficiency. Other objects and advantages of this inventionwill appear from the description thereof hereinafter following.

This application is a continuation-in-part of my earlier co-pendingapplication, Serial No. 426,281,1iled January 10, 1942, now abandoned.

The method of my invention involves, broadly, the contacting of certainplatinum metal compounds, more fully specified hereinafter, in aqueoussolution with certain types of supporting carriers in such manner thatthe platinum metal compound hydrolyzes and forms a firm and adherentdeposit of platinum metal oxide or hydroxide on the surface of suchcarrier, the oxide so formed being subsequently reduced to cats.-lytically active platinum metal. This method involves the utilization ofcompounds of platinum or palladium in which such platinum metal, 1. e.platinum or palladium, has a valency of 2 and the employment of carriermaterials in the form of certain dehydrated oxides.

The carrier thus employed in the production of the catalyst hereininvolved comprises a solid dehydrated, e. g. anhydrous, oxide of anelement taken from groups III to VIII of the periodic system, such aschromium oxide, zirconium dioxide, iron oxide, silica, dehydrated silicagel, or the like. In fact, the best carriers for the practice of myinvention are constituted by dehydrated earth metal oxides such forinstance as in particular aluminum oxide. The carrier specified must, ofcourse, be insoluble in water and should not comprise a precious metaloxide.

The compound of platinum or palladium in aqueous solution, employed inthe method of the invention, is a compound in which the platinum orpalladium has a valency of 2. Insofar as platinum compounds areconcerned I use, therefore, for instance the salts of thetetrachloroplatinic acid, e. g. the potassium salt, KzPtCh, containingtwo valent platinum, i. e. chlorocomplexes of the general formulaMezPtCl4, rather than the salts of the four valent platinic acid of thegeneral formula -Me2PtClc. Likewise, in the case of palladium, I usesalts of the two valent palladium, e. g. the sodium salt, NaaPdClq, oftetrachloropalladic acid. Other hydrolyzable salts of platinum orpalladium will readily suggest themselves to the experts in the art.

The hydrolysis of the platinum or palladium compound precipitates anoxide or hydroxide of platinum or palladium, respectively, on thespecified carrier in a firmly adherent coating. The oxide or hydroxideof platinum or palladium is then reduced by suitable reducing agents,and the final catalyst obtained.

The following examples will illustrate the method according to myinvention:

Example 1 l g. aluminum oxide powder in its ignited form is suspended inwater and 5 ml. of a solution of sodium palladium chloride containing 50mg.

palladium are added. The aqueous mixture is boiled under stirring. Afirmly adhering coating Example 2 1 g. chromium oxide, as obtained forinstance by the ignition of ammonium bichromate, is suspended in waterand m1. of sodium palladium chloride solution containing 50 mg.palladium are added. 1 g. sodium bicarbonate dissolved in water is addedto the solution. The aqueous mixture is boiled until the solution iscolorless. The palladium oxide is reduced and the catalyst filtered anddried. The pH value of the solution was 8.

Example 3 g. activated alumina tablets are boiled with a wetting agent,filtered and washed. 5 ml. of an aqueous solution containing 50 mg.palladium in the form of sodium palladium chloride are added to thehalf-dry pellets and the aqueous mixture is boiled. After precipitation,the palladium oxide is reduced and the catalyst obtained. The pH valueof the solution was 5.5.

Example 4 5 g. of hard dehydrated silica gel are boiled in a solutioncontaining sodium bicarbonate, with or without a wetting agent, untilsubstantially all air has escaped from the fine pores of the gel. Thesilica gel is filtered off and slightly washed with water. 5 ml. of asodium palladium chloride solution containing 50 mg. palladium areadded, without further addition of water, and the aqueous mixture isboiled. After precipitating the palladium oxide and reduction thereof tometallic palladium, the catalyst is filtered and dried. In thiscase thesodium bicarbonate not only facilitates the hydrolysis of the palladiumcompound but also fills the pores of the silica gel so that thepalladium oxide precipitate is concentrated on the outer surface of thegel where maximum concentration of the metal is desirable for catalyticreactions. The sodium bicarbonate is removed by washing the catalysteither prior or subsequent to the reduction of the palladium oxide. ThepH value of the solution was 8.

Example 5 10 g. of activated alumina tablets are boiled with the aqueoussolution of a wetting agent, filtered and washed. 100 mg. KaPtChdissolved in 10 ml. water, are added to the half-dry tablets and thesolution is boiled. After precipitation the black platinous oxide isreduced and the catalyst is ready for use. The pH value of the solutionwas between 6 and 7.

The hydrolysis of the platinum or palladium compound usually requiresheating of the solution. In the case of aluminum oxide carriers thehydrolytic effect is produced by simply heating a suitable aqueoussolution of the hydrolyzable platinum or palladium compound, but inother cases, for instance where the carrier comprises dehydrated silicagel, the hydrolysis proceeds best when a suitable alkalizing agent, suchas sodium bicarbonate, is added to the solution.

The reaction taking place is primarily a hydrolysis. It was found, forinstance, that sodium palladium chloride, NazPdCh, dissolved in water,is of acid reaction nature which would not be expected of a complex saltof such formula, the acid reaction being due to the incipient hydrolysiswhich may be formulated as The equilibrium of this reaction is very muchin favor of the complex palladium salt on the left side of the formula,but it may shift, completely or almost completely, to the right side ifone of the components on the right side is removed. It was surprising tofind that aluminum oxide for instance serves this purpose. The highlyinsoluble character of dehydrated ignited aluminum oxide is generallyknown; in analysis, for instance, it withstands all acids, even aquaregia, and has to be melted with soda to form a water soluble compound.Itcan hardly be assumed, therefore, that the minute amount of acidformed by the incipient primary hydrolysis reacts with A: according toany such equation as Al2Oa+6HCl 2AlCla-l-3H20, and that by such reactionthe hydrolysis is made to progress. In this respect it may also be notedthat I could find no aluminum chloride in the filtrate. It is moreprobable that the aluminum oxide is capable of absorbing the primarilyhydrolyzed palladium on its surface, and that thus the palladiumhydroxide is continuously removed from the equilibrium and thereby thereaction caused to proceed from the left to the right, till completehydrolysis has taken place. It is a fact, regardless of the theoreticalexplanation, that while a sodium palladium chloride solution as suchstays a clear solution when boiled, the same sodium palladium chloridesolution is hydrolyzed under almost complete precipitation of thepalladium when boiled in the presence of the highly insoluble andchemically inactive dehydrated aluminum oxide. Not in all cases doesthis hydrolytic process proceed just by the addition of a dehydratedsolid oxide taken from groups III to VIII of the periodic system. Theastonishing fact that in boiling such a solution the hydrolyzedpalladium oxide is completely or almost completely attached to thesurface of the carrier, suggests that also in those cases adsorptionplays an important part in the reaction.

The coating of catalyst metal of the group consisting of platinum andpalladium on the carrier, as obtained by the hydrolytic process, isextremely firm and adherent. The method according to my invention isvery suitable for the production of highly active powder catalysts, butit is especially valuable for the manufacture of supported catalystshaving granular 0r preformed carriers such as pellets, tablets, pills,etc. The method also allows the production of catalysts havingchemically inert carriers which heretofore were mainly platinized bysoaking processes. Catalysts prepared by soaking, and deposition duringsubsequent reduction, contain the catalyst metal distributed through thewhole carrier, particularly in the case of compressed preformedcarriers, whereby the catalyst metal distributed within such carriers isinaccessible to the catalytic reactants, whereas catalysts produced inaccordance with my invention have the catalyst metal accumulated on thesurface only, even in the case of compressed preformed carriers, wherebyall such platinum or palladium is available for the catalytic reaction.One reason for the deposition of the platinum and palladium on thesurface only of the carrier is the great speed with which the hydrolysistakes place in the method of the invention so that the catalyst metalcompound has no opportunity to penetrate into any pores of the body ofthe carrier.

In order to make possible such hydrolysis at the surface of the carrieronly, and thus prevent the deposition of the catalyst metal within thepores or cavities of the carrier, the carrier must have basic, ratherthan acid, characteristics. The dehydrated oxide specified must,therefore, be of basic characteristics either inherently, as in the caseof earth metal oxide and zirconium dioxide, Or it must be made basic, ase. g. in case of silica gel which must be treated with an alkalizingagent, such as bicarbonate of soda, prior to contacting it with thecatalyst metal solution.

The specified method is simple and economical, and is thereby alsohighly superior to the production of supported catalysts by a fusionmethod entailing high temperature and the use of aggressive salt melts,which would destroy many carriers, which as for instance activatedalumina can easily be plantinized or palladized according to myinvention.

The reduction of the platinum or palladium oxide to catalytically activemetal takes place in any suitable manner either before use as catalystor simultaneously with its use as hydrogenation catalyst except thatsuch reduction should not be accomplished by heat. Preferably suchreduction takes place immediately after completion of the hydrolysis andwhile the catalyst is still immersed within the hydrolysis solution,being accompanied therein by the addition of suitable reducing agents e.g. hydrazine salts, sodium formate, etc.

The prime feature of my invention is that it permits the production ofhighly active supported catalysts involving dehydrated oxide carriers asdescribed. A dehydrated silica gel catalyst, containing 50 mg.palladium, prepared by the method according to my invention liberated1600 ml. hy-

rogen in 50 min. in the liquid stage dehydrogenation oftetrahydronaphthalene, as compared with 210 ml. hydrogen developed froma like solution in like time by a catalyst of dehydrated silica gel,also containing 50 mg. palladium, but prepared by soaking the silica gelcarrier in a sodium palladium chloride solution and following reductionto palladium. In the hydrogenation of nitrobenzene 1 g. of a palladiumcatalyst in accordance with my invention consisting of a ferric oxidecarrier containing 5% palladium by weight causes the absorption of 560ml. hydrogen in 5 min., and 1 g. of a palladium catalyst produced inaccordance with my invention consisting of a zirconium dioxide carrierand containing 5% palladium by weight causes the absorption of 690 m1.hydrogen in 5 min. In another experiment involving the dehydrogenationof tetrahydronaphthalene a palladium catalyst produced in accordancewith my invention by hydrolyzing 100 mg. potassium platinous chloride ina ml. aqueous solution in the presence of 10 g. aluminum oxide tabletsliberated 600 ml. hydrogen from the boiling tetrahydronaphthalene in 50min.

The catalytic activity of catalysts prepared in accordance with myinvention and embodying the specified chemically inactive dehydratedoxide carriers is highly superior to that of catalysts prepared byreacting platinum metal solutions with chemically active carriers suchas freshly precipitated hydroxides. I have found, for instance, that apalladium catalyst comprising 1 g. of a carrier of ignited aluminumoxide and 5% by weight of palladium prepared in accordance with myinvention, caused the absorption of 5'70 ml. hydrogen in 5 min. in thereduction of nitrobenzene, whereas a palladium catalyst comprising 1 g.of a carrier of aluminum hydroxide and 5% by weight of palladium,produced by reacting a palladium salt in aqueous solution withchemically active aluminum hydroxide, caused the ab-- sorption of only150 ml. hydrogen in 5 min. in the reduction of nitrobenzene.

The pH value of the platinum or palladium compound solution employed inthe hydrolysis method of producing supported catalysts in accordancewith the invention has an important bearing on the degree of catalyticefliciency of the resultant catalyst. In the case of palladium catalystsI have found that the solution should preferably have a pH value withinthe range of about 5 to about 12. Thus, for instance, in thehydrogenation of a 100 cc. methanol solution containing 4 cc.nitrobenzene, the hydrogen absorption in the presence of a 5% palladiumactivated alumina catalyst produced by hydrolysis of sodium palladiumchloride amounted to 570 co. in the case of a catalyst produced from asolution having a pH value of 4.6 and to 860 cc. and 820 cc.,respectively, in cases of like catalysts produced from like aqueoussolutions hava pH value of 8 and 11, respectively. Thus in such case itis desirable to neutralize any acid set free in the hydrolysis, as forinstance by adding sodium bicarbonate. On the other hand, in the case ofplatinum catalysts, I have found that the solution should preferablyhave a pH value within the range of about 1 to about 8. Thus forinstance in the hydrogenation of 100 cc. methanol solution containing 4cc. nitrobenzene, the hydrogen absorption in the presence of a 1%platinum activated alumina catalyst produced by hydrolysis of potassiumplatinous chloride amounted to 260 cc. where the catalyst employed hadbeen produced from an aqueous solution having a pH value of 10, but to440 00., 810 cc. and 860 cc. where the catalyst had been produced inlike manner from a like solution having a pH value of 8, 4.6 and 3.5,respectively. It would appear, therefore, that the efilciency of thecatalyst tends to increase with increasing pH value of the solution inthe case of palladium catalysts and with decreasing pH value of thesolution in the case of platinum catalysts. In the experiment justmentioned involving the utilization of 5% palladium and 1% platinumactivated alumina catalysts, there were used in such experiment 25 mg.palladium and platinum, respectively, as catalyst metal. It is importantfor the emciency of the catalyst that such DH value is maintained duringthe reduction of the platinum oxide or palladium oxide formed during thehydrolysis.

The catalysts produced by the practice of the method of my invention canbe used in various catalytic processes, e. g. oxidation, polymerization,synthesis, hydrogenation or dehydrogenation processes, etc., althoughthey are specially useful for the reduction of oxygen or oxygencontaining compounds.

The method of producing supported catalysts according to my inventionprovides, therefore, catalysts of extremely high catalytic efliciency.Catalysts produced by such method do not suffer from impairment ofcatalytic activity experienced with supported catalysts wherein thecatalyst metal deposit is produced on the carrier by reduction ofplatinum or palladium compounds directly from a solution or by soakingthe carrier with the platinum or palladium compound solution andreducing the compound by heat. The method according to my invention isof particular benefit for supported catalysts embodying the specifieddehydrated oxide carriers where it is calculated to produce particularlyadvantageous results. The term "oxide as herein used in connectlon withplatinum and palladium includes not only oxides as such, but alsohydroxides. The term non-precious as herein used means elements notbelonging to the group of precious metals consisting of platinum metals,gold and silver. 9

What I claim is:

1. The method of producing a supported catalyst, comprising hydrolyzinga compound of catalyst metal taken from the group consisting of platinumand palladium, said compound containing said catalyst metal in the twovalent state, in an aqueous solution in the presence of a carrier ofsolid water insoluble dehydrated basic oxide of a non-precious elementtaken from groups III to VIII of the periodic system, and therebyprecipitating an oxide of said catalyst metal on the surface of saiddehydrated oxide carrier by hydrolysis of said compound of catalystmetal at such surface only, and reducing said catalyst metal oxide tocatalytically active catalyst metal.

2. The method of producing a supported catalyst, comprising hydrolyzinga compound of catalyst metal taken from the group consisting of platinumand palladium, said compound containing said catalyst metal in the twovalent state, in an aqueous solution in the presence of a carrier ofdehydrated aluminum oxide, and thereby precipitating an oxide of saidcatalyst metal on the surface of said dehydrated oxide carrier byhydrolysis of said compound of catalyst metal at such surface onlywithout substantial penetration into the body of said carrier, andreducing said catalyst metal oxide to catalytically active catalystmetal.

3. The method of producing a supported catalyst comprising hydrolyzing acompound of palladium in the two valent state in an aqueous solution inthe presence of a carrier of activated alumina, thereby precipitating anoxide of palladium on the surface of said activated alumina carrier byhydrolysis of said compound of palladium at such surface only, andreducing said palladium oxide to catalytically active palladium.

4. The method of producing a supported catalyst comprising hydrolyzing acompound of palladium in the two valent state in an aqueous solution inthe presence of a carrier of solid water insoluble dehydrated basicoxide of a nonprecious element taken from groups III to VIII of theperiodic system, thereby precipitating an oxide of palladium on thesurface of said dehydrated oxide carrier by hydrolysis of said compoundof palladium at such surface only, and reducing said palladium oxide tocatalytically active palladium within said solution, said solution atleast during said reduction having a pH value of from about to about 12.

5. The method of producing a supported catalyst comprising hydrolyzing acompound of platinum in the two valent state in an aqueous solution inthe presence of a carrier of solid water insoluble dehydrated basicoxide of a non-precious element taken from groups III to VIII of theperiodic system, thereby precipitating an oxide of platinum on thesurface of said dehydrated oxide carrier by hydrolysis of said compoundof s platinum at such surface only, and reducing said platinum oxide tocatalytically activeplatinum within said solution, said solution atleast during said reduction having a pH value of from about 1 to about8.

6. The method of producing a supported catalyst, comprising hydrolyzlnga compound of catalyst metal taken from the group consisting oi platinumand palladium, said compound containing said catalyst metal in the twovalent state, in an aqueous solution in the presence of a carrier ofsolid water insoluble dehydrated inherently basic oxide of anon-precious element taken from groups III to VIII of the periodicsystem, and thereby precipitating an oxide of said catalyst metal on thesurface of said dehydrated oxide carrier by hydrolysis of said compoundof catalyst metal at such surface only, and reducing said catalyst metaloxide to catalytically active catalyst metal.

7. The method of producing a supported catalyst, comprising hydrolyzinga compound of catalyst metal taken from the group consisting of platinumand palladium, said compound containing said catalyst metal in the twovalent state, in an aqueous solution in the presence of a carrier ofinsoluble dehydrated inherently basic oxide taken from the groupconsisting of earth metal oxide and zirconium dioxde, therebyprecipitating an oxide of said catalyst metal on the surface of saiddehydrated oxide carrier by hydrolysis of said compound of catalystmetal at such surface only, reducing said catalyst metal oxide tocatalytically active catalyst metal.

8., The method of producing a supported catalyst, comprising hydrolyzinga compound of palladium, said compound containing palladium in the twovalent state, in an aqueous solution in the presence of a carrier ofinsoluble dehydrated inherently basic oxide taken from the groupconsisting of earth metal oxide and zirconium dioxide, therebyprecipitating palladium oxide on the surface of said dehydrated oxidecarrier by hydrolysis of said compound oi palladium at such surfaceonly, reducing said palladium oxide to catalytically active palladiummetal.

EDGAR F. ROSENBLA'I'I.

REFERENCES CITED The following referenlces are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,111,502 Schwarcman Sept. 22,1914 1,215,396 Mittasch et al Feb. 13, 1917 1,222,260 Paal Apr. 17, 19171,739,306 1 Holmes Dec. 10, 1929 1,828,380 Rotger et al. Oct. 20, 19312,200,522 Streicher May 14, 1940 2,330,664 Bennett et al. Sept. 28, 19482,383,216 Treischmann Nov. 2, 1943 FOREIGN PATENTS Number Country Date436,906 Great Britain Oct. 21, 1935 477,026 Great Britain Dec. 16, 1937

